1. Field of the Invention
The present invention relates generally to a grinding wheel which is rotated by a drive shaft (wheel spindle) to grind a workpiece, and more particularly to such a grinding wheel that has a function of monitoring its grinding conditions and a function of automatically establishing a dynamic balance thereof.
2. Discussion of the Prior Art
A known grinding machine has grinding wheel which includes a cylindrical core portion which is mounted on a drive shaft, and an annular abrasive portion fixed to the outer circumferential surface of the core portion. The grinding wheel is adapted to grind a workpiece in contact with the abrasive portion while the wheel is rotated by the drive shaft. Generally, the grinding wheel is required to maintain the dynamic balance. To this end, it is necessary to monitor the state of the wheel during its grinding operation. When the abrasive portion of the wheel is made of highly durable abrasive grains, such as diamond or CBN (cubic boron nitride), which permit highly efficient grinding, the grinding wheel tends to suffer from imbalance, and chattering, burning or cracking phenomena, which occur due to relatively high hardness of the abrasive grains. Accordingly, it is required to carefully monitor the grinding wheel for promptly dealing with such abnormal conditions as described above.
Conventionally, there is proposed a device for eliminating dynamic imbalance of the rotating grinding wheel, by providing the wheel with a balancing member or weight an automatically calculating the amount of movement of the balancing member along the circumference of the wheel to establish the dynamic balance, and displaying the calculated amount, as disclosed in laid-open publication No. 60-259927 of unexamined Japanese Patent Application. However, since the imbalance of the wheel must be rectified by manually moving the balancing member after the wheel is stopped, it requires a lot of time to balance the wheel, and the operating efficiency of the grinding machine is accordingly lowered. Further, since the wheel balancing cannot be effected while the wheel is rotating, the unbalanced rotating wheel would have excessive wear in local portions on the outer circumferential surface thereof, which leads to poor grinding accuracy and lowered durability of the wheel.
It is also proposed to provide an acoustic-wave sensor (AE sensor) for detecting high-frequency ultrasonic vibrations (acoustic or elastic emissions) which are generated by the grinding wheel, as disclosed in Publication No. 64-278 of examined Japanese Utility Model Application. The disclosed AE sensor is fixed to a stationary member of the grinding machine, for detecting vibrations which are transmitted through a liquid that is jetted on a side surface of the abrasive portion of the grinding wheel. In this case, the vibrations detected by the sensor may be affected by the conditions in which the liquid is jetted against the abrasive portion, or by gases which are present in the liquid.
Conventionally, a temperature sensor is embedded in the workpiece to be ground by the grinding wheel, so as to measure a temperature at the grinding surface of the wheel during the grinding operation. However, the known sensor is not able to accurately measure the wheel temperature since the workpiece having the sensor is moved relative to the rotating wheel during the grinding operation. If the vibrations or the wheel temperature cannot be accurately detected as in the conventional grinding machine, it is difficult to determine abnormalities in the grinding, resulting in increased unacceptance or reject ratio of the ground workpieces. Further, the above manner of measuring the wheel temperature is restricted by the manner of grinding and the configuration of the workpiece. For example, it is difficult to embed the temperature sensor in a cylindrical workpiece which is rotated during the grinding operation.